hi all please help me...
hi all please help me...
(OP)
Dear All
Is it correct if i take the advantage of soil weight while sizing the footing subjected to upward loads and moments? Please correct me and provide me the source if possible.
best regards
MVV






RE: hi all please help me...
dont forget that these loads need to be factored down by 0.6 to 0.9 depending on the code.
RE: hi all please help me...
Dik
RE: hi all please help me...
Taking advantage of the soil may reduce the possiblity of stability failures but Adding weight to your footing will contribute to the increase of reinforcement to the footing itself so dont forget to check ultimate
You may also consider passive pressures.
Regards,
E104909
RE: hi all please help me...
You would have to explain that one to me. Adding mass on top of a footing doesn't increase the reinforcement requirement. And passive pressure doesn't help with resisting uplift, as passive pressure results in a lateral force.
RE: hi all please help me...
If the footing is picking up soil loads to resist uplift, extra reinforcing, beyoud the normal bottom reinforcing, will be adviseable if not outright required in the top to develop the soil load. Otherwise, you're kidding yourself.
Other than that, I agree.
Mike McCann
MMC Engineering
RE: hi all please help me...
I did not say checking of uplift. I just genereralized it. Overturning would be the concern. Adding mass to the top of footing means adding pressure to your footing. Slip is possible too. Now, structurally your footing should be checked..and geotechnical check to consider layers of soil is also needed for the realistic check of slip failure.
Now reinforcement is a differrent thing. As you go deeper the height of soil goes deeper and your reinfircement as msquared says will increase. Now depends on the level of water table that produces the uplift. Compare 9.81 with 18. Soil is still higher.
Everything will depend on the actual condition.
Regards,
E104909
RE: hi all please help me...
RE: hi all please help me...
Mike McCann
MMC Engineering
RE: hi all please help me...
The soil 'has always been there' and the strength measured already has it in place and the weight of the concrete is nearly equal to the weight of the soil displaced (unless foundation design is critical enough that this has to be considered and for caissons I often include the weight of the concrete due to the concentrated load).
Dik
RE: hi all please help me...
RE: hi all please help me...
Is there a chance that the confusion here is whether the designer uses the net soil pressure or the gross soil pressure in designing the reinforcing?
RE: hi all please help me...
RE: hi all please help me...
RE: hi all please help me...
Interesting!
Regards,
E104909
RE: hi all please help me...
RE: hi all please help me...
Dik
RE: hi all please help me...
RE: hi all please help me...
At one end of the footing you will have very low bearing pressures that will (likely) not be enough to counter the combined wieght of the concrete and soil above the footing in that area. You would therefore have negative bending at the the "heel" (for lack of a better term) and postive bending at the "toe" in the uplift condition.
For a concentric gravity load above the footing, I agree that you do not need to increase the reinforcement regardless of if there is 1 ft or 10 ft of soil above the ftg. becuase the soil load gets passed straight down through the footing.